Variable compression system for internal-combustion engines



April 15, 1952 R. SKINNER 2,592,829

VARIABLE COMPRESSION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed May 21, 1948 2 SHEETS-SHEET 1 IN V EN TOR.

vrfaPA/ZKST L SKINNER 2,592,829

R. VARIABLE COMPRESSION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed May 21, 1948 2 SHEETSSHEET 2 April 15, 1952 J; 50 9/ V \L INVENTOR. 7; 24591 A n.5'%znrzez' Patented Apr. 15, 1952 OFFICE VARIABLE COMPRESSION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Ralph L. Skinner, Detroit, Mich. Application May 21, 1948, Serial No. 28,478

8 Claims. (Cl. 123-48) This invention relates broadly to internal-combustion engines and more particularly to a novel mechanism for varying the compression ratio of such engines.

An important object of the present invention is to provide a novel mechanism for varying the compression ratio of an internal-combustion engine either manually or automatically while the engine is in operation.

Another object of the invention is to provide a mechanism of the above-mentioned character that can be readily adapted to slide-valve engines without interfering in any way with operation of the valves or with the intake or exhaust ports of the engine.

Still another object of the invention is to provide a mechanism for varying the compression ratio of an internal-combustion engine in such manner that maximum power can be obtained at anydesired engine speed.

Yet another object of the invention is to provide a mechanism for varying the compression ratio of an internal-combustion engine so as to obtain maximum torque at any desired engine speed.

A further object of the invention is to provide a mechanism for varying the compression ratio of an internal-combustion engine so as to obtain maximum fuel economy.

A still further object of the invention is to provide means for varying the compression ratio of an internal-combustion engine so as to permit the use of different grades of fuel in the engine.

A yet further object of the invention is to increase the over-all efficiency and fuel economy of internal-combustion engines.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the drawings forming a part of this specification and wherein like numerals are employed to designate like parts throughout the same,

Fig. 1 is a vertical, transverse sectional view Contrariwise, it is desirable to have the compression ratio as high as is possible without causing detonation or knocking when the engine is operating under conditions where the load is great, as during rapid acceleration. In certain types of internal-combustion engines this effect can best be obtained by providing a vertically movable cylinder head and means to adjust the head in such manner as to varythe volume of the compression chambers. The invention is here shown embodied in and associated with an internal-combustion engine of the slide-valve type.

Considered in certain of its broader aspects, the embodiment of the invention here shown by way of illustration comprises an inner cylinder head H] which is vertically adjustable against the action of a spring [2, and it will be observed that a portion of this head extends into the cylinders above the power pistons M. The latter portions of the head H] are sealed by essentially thin metal reeds or rings 16 to maintain closed combustion chambers l8 above the pistons M. A stationary outer cylinder head .20 slidably supports the inner head 10 and forms a seat for the coil spring l2.

The head 10 can be adjusted vertically to vary the compression ratio of the engine either manually or automatically through suitable mechanical or hydraulic mechanism. In the form of the invention shown, the head it is adjusted automatically and hydraulically. To this end the inner and outer heads l0 and 20 are formed to provide a hydraulic cylinder 22 therebetween, which cylinder is hydraulically sealed by rings 24 and 25. Oil or the like is introduced into the annular space between seals I6 and 26 through pipe 23 and passage 25 to lubricate such seals. By reason of this construction the compression ratio of the engine can be varied by regulating the hydraulic pressure in the hydraulic cylinder. As the pressure increases, the inner head It moves downwardly against the action of spring [2 and increases the compression ratio. On the other hand, as the pressure decreases, the spring I? retracts the head in and decreases the compres-- sion ratio. In this connection it is important that the sealed-in area of the head til, i. e., the portion inclosed within the thin metal sealing rings It, be larger than the area of combustion chamber 18 and power piston it so that a relatively slight vertical movement of the head ii) effects a relatively great change in combustion ratio. This is essential from an operating and a commercial standpoint, since a long vertical travel of the head is impracticable. By reason of the instant construction, I have been able to in- 3 crease the compression ratio of the engine from 12 -1 to 20-1 by moving the head approximately .225 inch.

In the particular hydraulic system here shown for moving the head it], hydraulic liquid is drawn from a supply tank 28 through pipe 29 by a pump 30 and is discharged to the hydraulic cylinder 22 through pipe 3!, a control valve designated gen erally by the numeral 32, pipe 34, and oil passage 3E. The valve 32 is in communication with the intake manifold 38 of the vehicle through a vacuum line 40 and is controlled thereby to regulate the hydraulic pressure in the cylinder 22. The arrangement is such that the passage through the valve is relatively restricted when the vacuum in the intake manifold is relatively low and is more or less unrestricted when the vacuum in the intake manifold 38 is relatively great. Vacuum in the intake manifold 38 is high When the vehicle is idling or operating under conditions where the load is not excessive. Under these conditions the valve 32 will be wide open to admit full hydraulic pressure to the cylinder 22 and thus force the inner cylinder head It downwardly to reduce the volume of the compression chambers above the power pistons M. In other words, under these conditions a high compression ratio is obtained. On the other hand, when the vehicle is operating under a relatively high load as during rapid acceleration and the vacuum in the intake manifold 38 is relatively low, the control valve 32 substantially closes and the pressure in the hydraulic cylinder 22 is reduced. Under these conditions the spring l2 retracts the inner head l and increases the volume of the compression chamber 18. Thus when the conditions last described prevail, a relatively low compression ratio which is suitable for the fuel being used obtains in the engine.

With the above as a general introduction to the construction and operation of the engine here shown, it is believed that a more detailed description is in order in which attention is given to particular details of construction which embody special features of the invention,

One detail of construction which deserves particular emphasis is the means herein provided for maintaining the inner head freely movable at all times. Heretofore attempts have been made to vary the compression ratio of internal-combustion engines by adjusting the cylinder head or a portion thereof to vary the clearance volume of the compression chambers, but these efforts have been generally unsuccessful in practice due to the fact that carbon and other deposits form on the sliding parts and eventually bind or freeze the same so that they function improperly or not at all. In this connection it will be readily apparent that since the moving parts are exposed to the combustion chambers, the obstructing deposits form relatively rapidly. In the instant construction the thin metallic sealing members [6 which close off the combustion chambers l8 are carried by the movable inner head It. These members l6 are formed with relatively thin shear edges which scrape along the bearing surfaces which support the head 10 during movement of the latter and keep carbon and other materials from accumulating in amounts sufficient to freeze or bind the head. Moreover, by reason of the essential thinness of the metal sealing reeds l6 and the fact that the outer marginal portions thereof are normally under tension, explosion waves which result when the fuel charge is fired in the combus= 4 tion chamber (8 impinge against the projecting outer marginal portions of the reeds and set up vibrations therein which materially assist the shear edges of the reeds in maintaining the relatively movable surfaces free of incrustation.

Also, the elements which provide the bearing surfaces for the head H) are uniquely constructed to create vibrations in response to explosions in the combustion chambers I8, which vibrations assist the shear edges of sealing means 16 in preventing formation of the obstructing deposits. The merit of this construction has been demonstrated by actual tests, and the performance of the engine under actual operating conditions farsurpasses any prior construction within my knowledge.

As suggested, Fig. 1 is a vertical, transverse sectional view through one cylinder of amulticylinder slide-valve engine, and this figure illustrates an internal cylinder 42 disposed verticallyin the cylinder block 44 and slidably supporting the power piston l4. Surmounting the cylinder 42 is a ported ring 46 having the usual fuel inlet 48 and fuel outlet 59 which are controlled by slide valves 52 and 54 in the conventional manner. Above and resting upon the ring 46 is a hold-down ring 56 which is pressed downwardly by an annular spring Washer 58 of the Belleville type. As clearly shown in the drawing, the washer 58 is disposed in an annular chamber 60 between the outer cylinder head 20 and the cylinder block M. When the outer cylinder head 20 is tightened against the block, it presses downwardly against the spring washer 58, and the latter in turn acts against the holddown ring 56, ring 46, and cylinder 42 to hold the cylinder pressed solidly against the usual support 62. Cooling water is circulated through the outer cylinder head 20 and cylinder block 44 in the conventional manner. Seals 64 and 66 are provided between the inner cylinder head If! and the outer cylinder head 20 to prevent the coolant water from entering the hydraulic cylinder 22 and from escaping through the top of the head between the inner and outer members I0 and 20.

According to the present invention the inner cylinder I 0 extends upwardly above the outer head 20, and the projecting portion thereof carries a nut 68 which co-operates with the head 26 to confine the spring 12. In this connection it will be readily apparent that the spring 12 can be selectively ten'sioned by tightening or loosening the nut 68.

Preferably each of the sealing members 16, 24, 25, B4, and 66 comprises a plurality of thin metal reeds or annuluses which are generally frustoconical in shape and are nested one within the other. These reeds are effective for sealing the joints between the relatively movable parts and are particularly effective for resisting hydraulic pressure.

The collective reeds in each seal are suitably clamped at the inner margins thereof and in each instance the outer peripheral edges of the individual, thin reeds are held in pressed frictional engagement with the confronting surface of a surrounding member. More particularly, in the particular arrangement here shown by Way of illustration, the head I0 is formed with an outwardly and downwardly inclined surface I00 which backs up and supports the reeds 15 from above, and the reeds are clamped solidly against the surface I08 by an annular threaded ring I02. A downwardly and outwardly inclined surface 104 on the ring I62 is substantially parallel to and co-operates with the back-up surface I to clamp the reeds H solidly on the head I0, and the reeds are flexed over the edge of the surface I04 to assure pressed engagement thereof with the ring 5 8. The reeds approach the frictionally engaged surface obliquely, and the thin, knifelike edges of the individual reeds maintain a highly effective fluidtight joint between the parts and at the same time permit the parts to be readily moved relative to each other.

In addition to the above, the individual, thin reeds or annuluses which make up the seal l5 together with vibrations created in the reeds by explosion waves from the combustion chamber l8 perform the highly important function of keeping the reeds and the adjacent and contiguous inner surfaces of the hold-down ring 56 free from carbon and other deposits which collect thereon during operation of the engine. In this connection it will be observed that the top surface I04 of clamping ring W2 is cut back as at I06 or recessed away from the outer marginal portions of the reeds so that a relatively large area of the bottom ring is exposed to explosions and pressure changes occurring in the combustion chamber. These explosions and pressure changes create vibrations in the reeds 16 which assist the shear edges there-of in maintaining the relatively moving parts free from carbon, varnish, and other deposits. Heretofore a great deal of trouble has been encountered by these deposits which tend to bind or freeze the head or other part which is moved to vary the compression ratio of the engine. After a short time and frequently within half an hour of operating time, the exposed parts become so incrusted with carbon and the like that the mechanism for varying the compression ratio is rendered inoperative. I have found, however, that if a seal of the type hereinabove described is provided at IS, the thin outer edges of the reeds scrape against and along the holddown ring 55 during movement of the inner head ill to remove any carbon or other deposits as rapidly as they are formed and thus maintain the path of travel of the seal essentially free of incrustation. Actual tests have demonstrated that a variable compression head constructed in this manner will operate successfully for long periods of time without appreciable interference from incrustation.

Further, I have found that the effectiveness of the thin metal reeds in the seal I6 to prevent deposited varnish, carbon and the like from eventually binding or freezing the adjustable head I0 is unexpectedly enhanced by providing anannular, radial shoulder 10 on the inner wall of the hold-down ring 56 below the seal. It will be observed that the shoulder 10 faces upwardly and inwardly and that it communicates with the combustion chamber l8 through an annular passage 12. Thus, the shoulder Ill is exposed to the fuel explosions in the combustion chamber I8, and these explosions react against the shoulder to set up vibrations in the hold-down ring 56 which assist the shear outer edges of the thin metal annuluses or reeds in the seal I6 in preventing carbon and the like from accumulating to such an extent that the mechanism for varying the compression ratio of the engine is rendered inoperative.

Attention is now directed to Fig. 3 which shows the automatically controlled oil-pressure regulating valve 32. This valve comprises generally cylindrical body '14 having a side inlet [6 and an end outlet 18 which are connected by rightangularly disposed passages and 82. A valve seat 84 is provided at the juncture of the passages 80 and 82, and a valve 36 is slidably mounted in the wall 88 to engage the seat t l and to control flow through the body i l. Valve is urged against the seat 84 to shut off flow through the device by means of a spring 99 which is confined between an annular flange 92 on the stem portion of the valve and the end wall 94 of the valve body M. A Sylphon valve 96 is connected at one end to the valve 86 and at the other end thereof to the end wall 94. Also, the Sylphon 96 communicates with an opening 98 in the wall 94, which open-' ing in turn communicates with the intake manifold 38 of the engine through the suction line 40 in the manner hereinabove described. By reason of this arrangement, the Sylphon SE'is responsive to reduction of pressure in the intake manifold 38 to slide the valve 8% back and forth relative to the seat 84. As suggested, the inlet 16 is connected to the discharge side of the pump 10 by the pipe 3|, and the outlet 78 is connected to the passage 35 by pipe 34 so that flow of hydraulic liquid to and from the hydraulic cylinder 22 is controlled by the valve 32. Since the valve 32 is responsive to variations in pressure in the intake manifold 38 and since this valve controls the flow of fluid to and from the hydraulic cylinder 22, the inner cylinder head it will move up and down against the action of spring :2 in response to operating conditions in the intake manifold.

As will be readily apparent, it is desirable to have a relatively high-compression ratio when the load on the engine is relatively low. Also, it will be readily apparent that, under these conditions, a relatively high vacuum will exist in the intake manifold 38. The relatively high vacuum in the manifold acts through the Sylphon valve 96 to hold the valve 86 retracted substantially from the seat 84. Substantially maximum oil pressure is then developed in the hydraulic cylinder 22, and the inner cylinder head I0 is forced downwardly against the action of spring 52 to reduce the clearance volume of the compression chambers I 8 and thus increase the compression ratio. Manifestly, the inner cylinder head I ll will move downwardly until the forces acting thereon are in equilibrium. In this manner the head HE is automatically positioned according to the hydraulic pressure transmitted by the control valve 32 and that in turn is controlled by the vacuum in the intake manifold 38.

Conversely, when the engine is operating under conditions which demand a high power output as during rapid acceleration at any speed, there is less vacuum in the manifold and there is less force tending to retract the valve 88. Consequently, the spring'eil advances the valve toward its seat and thus reduces the pressure in the hydraulic cylinder 22. Whenever pressure in the hydraulic cylinder is reduced, the spring I2 retracts the inner cylinder head In until the forces acting thereon are again in equilibrium. As the inner cylinder head It rises or retracts, the clearance volume in cylinders l8 increases and the compression ratio is correspondingly reduced.

The regulating valve 32 is sufficiently sensitive so that proper compression ratios are obtained automatically under all operating conditions and the valve can be easily and quickly adjusted for different grades of fuel.

Having thus described the invention, I claim: 1. In combination with an internal-combustion engine having a combustion chamber and a power piston in said combustion chamber, inner and outer wall members collectively forming a top closure for said combustion chamber, said outer wall member being disposed around and spaced circumferentially from the inner wall member and the latter being adjustable to vary the clearance volume of the combustion chamber, at least one essentially thin, annular, frusto-conical, flexible and resilient sealing reed interposed between the wall members, and means mounting said reed on one of said wall members with the edge of the reed bearing at an oblique angle against the other of said wall members, said mounting m ans having an under supporting surface for the reed and the latter being flexed over the edge of the supporting surface to press the edge of the reed solidly against the surface on which it edgewise bears, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to said other wall and said bevel edge adapted to scrape along the wall surface engaged thereby during movement of said inner wall member whereby to keep said wall surface free from carbon and other deposits which accumulate during operation of the engine and tend to bind or freeze said inner wall member, a portion of the supporting surface adjacent to the wall engaged by the bearing edge of the reed being recessed away from the reed and exposing a relatively large area of the reed to explosions and pressure changes in the combustion chamber whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like.

2. In combination with an internal-combustion engine having a combustion chamber and a power piston in said combustion chamber, inner and outer wall members collectively forming a top closure for said combustion chamber, said outer wall member being disposed around and spaced circumferentially from the inner wall member and the latter being adjustable to vary the clearance volume of the combustion chamber, at least one essentially thin, annular, frusto-conical flexible and resilient sealing reed interposed between the wall members, and means mounting said reed on one of said wall members at an oblique angle to the other of said wall members, said mounting means having an under supporting surface for the reed and the latter being flexed over the edge of the supporting surface to press the edge of the reed solidly against the surface on which it edgewise bears, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to the wall against which it bears, said bevel edge adapted to scrape along the wall surface engaged thereby during movement of said inner wall member whereby to keep said wall surface free from carbon and other deposits which accumulate during operation of the engine and which tend to bind or freeze said inner wall member, a portion of said bearing surface adjacent the wall engaged by the bearing edge of the reed being recessed away from the reed and exposing a relatively large area of the reed to explosions and pressure changes in the combustion chamber whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like, said mounting also having a top supporting surface for the reed, which surface extends substantially entirely across and flatly engages the reed to back up and reinforce the same and to prevent buckling thereof under explosions and pressure changes in the combustion chamber and by scraping action of the reed during adjustment of said inner wall member.

3. In combination with an internal-combustion engine having a combustion chamber and a power piston in said combustion chamber, inner and outer wall members collectively forming a top closure for said combustion chamber, said outer wall member being disposed around and spaced circumferentially from the inner wall member and the latter being adjustable to vary the clearance volume of the combustion chamber, at least one essentially thin, annular, frusto-conical sealing reed interposed between the wall members, means mounting said reed on one of said wall members at an oblique angle to the other of said wall members, said mounting means having an under supporting surface for the reed and the latter being flexed over the edge of the supporting surface to press the edge thereof solidly against the surface on which it bears, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to the wall, said bevel edge adapted to scrape along the wall surface engaged thereby during movement of said inner wall member whereby to keep said wall surface free from carbon and other deposits which accumulate during operation of the engine and which tend to bind or freeze said inner'wall member, a portion of said bearing surface adjacent the wall engaged by the bearing edge of the reed being recessed away from the reed and exposing a relatively large area of the reed to explosions and pressure changes in the combustion chamber, whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like, said mounting also having a top supporting surface for the reed, which surface extends substantially entirely across and flatly engages the reed to back up and reinforce the same and to prevent buckling thereof under pressures caused by explosions and by scraping action during adjustment of the inner wall member, and a radially inwardly extending shoulder on the wall member engaged by the scraping edge of said reed, said shoulder being exposed to explosions and pressure changes in said combustion chamber and operative in response to such explosions and pressure changes to create vibrations in the wall, said vibrationsco-operating with the scraping edge of the reed to prevent excessive amounts of carbon and other deposits from accumulating on said wall members.

I 4. In combination with an internal-combustion engine having a combustion chamber and a power piston in said combustion chamber, inner and outer wall members collectively forming a top closure for said combustion chamber, said outer wall member being disposed around and spaced ciroumferentially from the inner wall member and the latter being axially movable to vary the clearance volume of the combustion chamber, at least one essentially thin, annular, flexible and resilient sealing reed interposed between the wall members, and means mounting said reed on one of said wall members, said reed having at least a portion thereof disposed obliquely with respect to the other of said wall members and the edge of said oblique portion bearing against said other wall member, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to said other wall member and said bevel edge adapted to scrape along the wall surface engaged thereby during movement of said inner wall member whereby to keep the portion of the wall surface engaged thereby free from carbon and other deposits which accumulate during operation of the engine and tend to bind or freeze said inner wall member, said mounting means providing a back-up surface for the reed and said back-up surface extending substantially to the bearing edge of the reed, said mounting means also including retaining means engaging the undersurface of the reed, said retaining means terminating a substantial distance from the bearing edge of the reed to expose a relatively large area of the reed to explosions and pressure changes in the combustion chamber whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like.

5. In combination with an internal combustion engine having a combustion chamber and a power piston in said combustion chamber, inner and outer wall members collectively forming a top closure for said combustion chamber, said outer wall member being disposed around and spaced circumferentially from the inner wall member and the latter being axially movable to vary the clearance volume of the combustion chamber, at

least one essentially thin annular flexible and resilient sealing reed interposed between the Wall members, means mounting said reed on one of said wall members, said reed having at least a portion thereof disposed obliquely with respect to the other of said wall members and the edge of said oblique portion bearing against said other wall member, said mounting means providing a back-up surface for the reed and said back-up surface extending substantially to the bearing edge of the reed, the bearing edge of said reed being beveled to present an essentially sharp sealing and, scraping edge to said other wall member and said beveled edge adapted to scrape along the wall surface engaged thereby during movement of said inner wall member whereby to keep the portion of the wall surface engaged thereby free from carbon and other deposits which accumulate during operation of the engine and tend to bind or freeze said inner wall member, and retaining means engagin the undersurface of the reed.

6. A- cylinder head for variable compression engines provided with a chamber having an annular side wall and. opening through the undersurface thereof, said chamber positioned to register with the combustion chamber of an engine on which the head is adapted for use, a piston reciprocable in the chamber having an annular side wall spaced circumferentially from the annular wall of the chamber, at least one essentially thin annular flexible and resilient sealing reed interposed between the mentioned wall of the piston and the mentioned wall of the chamber, means mounting said reed on one of said and said back-up surface extending substantially -to the bearing edge of the reed, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to said other wall and said beveled edge adapted to scrape along the wall surface engaged thereby during movement of said piston whereby to keep the portion of said wall surface engaged by said reed free from carbon and other deposits which accumulate during the operation of the engine and tend to bind or freeze said piston, and retaining means engaging the undersurface of the reed.

7. A cylinder head for variable compression engines provided with a chamber having an annular side wall and opening through the undersurface thereof, said chamber positioned to register with the combustion chamber of an engine on which the head is adapted for use, a piston reciprocable in the chamber having an annular side wall spaced circumferentially from the an nular wall of the chamber, at least one essentially thin annular flexible and resilient sealing reed interposed between the mentioned wall of the piston and the mentioned wall of the chamber, and means mounting said reed on one of said walls, said reed having at least a portion thereof disposed obliquely with respect to the other of said walls and said oblique portion bearing edgewise against said other wall, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to said other wall and said beveled edge adapted to scrape along the wall surface engaged thereby during movement of said piston whereby to keep the portion of the wall surface engaged thereby free from carbon and other deposits which accumulate during operation of the engine and tend to bind or freeze said piston, said mounting means providing a back-up surface for the reed and said back-up surface extending substantially to the bearing edge of the reed, said mounting means also including retaining means engaging the under-surface of the reed, said retaining means terminating a substantial distance from the bearing edge of the reed to expose a relatively large area of the reed to explosions and pressure changes in the combustion chamber whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like.

8. A cylinder head for variable compression engines provided with a chamber having an annular side wall and opening through the undersurface thereof, said chamber positioned to register with the combustion chamber of an engine on which the head is adapted for use, a piston reciprocable in the chamber having an annular side wall spaced circumferentially from the annular wall of the chamber, at least one essentially thin annular flexible and resilient sealing reed interposed between the mentioned wall of the piston and the mentioned wall of the chamber, and means mounting said reed on one of said walls, said reed having at least a portion thereof disposed obliquely with respect to the other of said walls and said oblique portion bean ing edgewise against said other wall, said mounting means providing a back-up surface for the reed and said back-up surface extending sub stantially to the bearing edge of the reed, said mounting also having an under supporting surface for the reed and the latter being flexed over the edge of the supporting surface to press the edge of the reed solidly against the surface on which it edgewise bears, the bearing edge of said reed being beveled to present an essentially sharp sealing and scraping edge to said other wall and said beveled edge adapted to scrape along the wall surface engaged thereby during movement of said piston whereby to keep the portion of the wall surface engaged thereby free from carbon and other deposits which accumulate during operation of the engine and tend to bind or freeze said piston, a portion of the supporting surface adjacent to the wall engaged by the bearing edge of the reed being recessed away from the reed and exposing a relatively large area of the reed to explosions and pressure changes in the combustion chamber whereby said explosions and pressure changes create vibrations in the reed which assist in maintaining the reed and the wall engaged thereby free from carbon and the like.

RALPH L. SKINNER.

"12 REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date Re.18,5 95 Wilson Sept. 13, 1932 1,871,242 Skinner Aug. 9, 1932 1,871,250 Walrath Aug. 9, 1932 2,120,012 Andreau June 7, 1938 2,182,105 Woodward Dec. 5, 1939 FOREIGN PATENTS Number Country Date 2,015 Great Britain Jan. 27, 1909 483,298 Great Britain July 13, 1936 866,206 France Apr. 15, 1941 

